Valve Seat & Guide Machining

The most critical sealing surface in the valve train assembly is between the face of the valve and its seat in the  cylinder head when the valve is closed. Leakage between these surfaces reduces engine compression and power  and can lead to valve burning. To ensure proper seating of the valve, the valve seat must be:

  • Correct width.
  • Correct location on the valve face.
  • Concentric with the guide (less than .002˝ runout).

The ideal seat width for automotive engines is 1/16˝ for intake valves and 3/32˝ for exhaust valves. Maintaining this  width is important to ensure proper sealing and heat transfer.

Just as important is the correct angle of the actual faces on the seat, a valve seat with different face angles to the  corresponding valve would be next to useless.

The diagram alongside shows the valve seat angles for an Exhaust Valve Seat.

  1. Upper Correction Angle 70° (on an Inlet Valve Seat this is 75°)
  2. Valve Seat Angle 45°
  3. Lower Correction Angle 30°
  4. Valve Seat Width


Cutting valve seats requires an accurate  machining process to ensure that the  minimumamount of material is removed while achieving the correct seat width and angles.
Here at Auto Services we use a Serdi 3.0for our  valve  seat and valve guide machining.


All 3 angles on the valve seat are cut in one pass  allowing us to give  our customers the very best  machining
service available with a price  to match.


We can machine the valve seats on the majority of  cylinder heads, please call for latest prices.